In patent application, assigned to the assignee of this application, Ser. No. 214,481, Dec. 9, 1980, Muller et al. (to which German application No. P 30 01 711.9 corresponds), there is proposed a sensor system for detecting the oscillations that occur during detonations of an internal combustion engine, using at least one optical sensor, preferably a glass rod or a light-conducting cable made of glass fibers. The optical sensors are then integrated with the spark plug, attached to a pre-chamber or inserted into the cylinder head gasket.